An explorer-in-residence at the National Geographic Society, Davis has written nine books, made prize-winning TV programs and documentaries, and widely published his photographs. National Geographic has just issued Light at the Edge of the World, a book of photographs and essays documenting his journeys among vanishing cultures.

Davis and Chris Rainier, a photographer, have teamed up with two Web specialists to develop Cultures on the Edge, an online site to raise global awareness about threatened cultures around the world.

In a telephone interview, Davis talked with National Geographic News about his work and passions.

You're a passionate advocate of the need to ensure the survival of cultural diversity. Why does diversity matter, if nature and society are changing all the time anyway?

Just as there is a biological web of life, there is also a cultural and spiritual web of lifewhat we at the National Geographic have taken to calling the "ethnosphere." It's really the sum total of all the thoughts, beliefs, myths, and institutions brought into being by the human imagination. It is humanity's greatest legacy, embodying everything we have produced as a curious and amazingly adaptive species. The ethnosphere is as vital to our collective well-being as the biosphere. And just as the biosphere is being eroded, so is the ethnosphereif anything, at a far greater rate.

Some people say: "What does it matter if these cultures fade away." The answer is simple. When asked the meaning of being human, all the diverse cultures of the world respond with 10,000 different voices. Distinct cultures represent unique visions of life itself, morally inspired and inherently right. And those different voices become part of the overall repertoire of humanity for coping with challenges confronting us in the future. As we drift toward a blandly amorphous, generic world, as cultures disappear and life becomes more uniform, we as a people and a species, and Earth itself, will be deeply impoverished.

You argue that the steady loss of languages, which are reportedly disappearing at a rate of one every two weeks, is an alarming indicator of declining cultures. What do languages represent that makes you so fiercely concerned about their demise?

Language isn't just a body of vocabulary or a set of grammatical rules; it's a flash of the human spirit, the vehicle through which the soul of each particular culture comes into the material world. When you and I were born there were 6,000 languages spoken on Earth. Now, fully half are not being taught to schoolchildren. Effectively, they're already dead unless something changes. What this means is that we are living through a period of time in which, within a single generation or two, by definition half of humanity's cultural legacy is being lost in a single generation. Whereas cultures can lose their language and maintain some semblance of their former selves, in general, it's the beginning of a slippery slope towards assimilation and acculturation and, in some sense, annihilation.

You talk about the need to preserve traditional cultures, but preserve at what level? We can't really expect cultures not to change, mainly to satisfy our curiosity.